The present disclosure relates to calibrating a printing process, and more particularly, to calibrating a printing process based on multiple interrogations of a calibration patch occurring between various printing functions.
Current electrophotographic (EP) printing processes require calibration in order to maintain acceptable print quality. An EP process generally includes an imaging process and an image transfer process. The imaging process includes placing an image on an intermediate transfer element (e.g., a photoconductor drum or a transfer belt) and developing the image with a marking agent, such as a dry toner. The transfer process generally includes transferring and fusing the image to a print medium such as paper or a transparency. Calibrating an EP printing process helps account for process variations caused by problems such as the deterioration of a photoconductor drum or transfer belt within the EP printing device.
Conventional EP printing devices calibrate the printing process by comparing a measured amount of marking agent from a calibration patch with an expected amount. A calibration patch is typically a square shaped area filled to a certain density or percentage level with a marking agent. The patch is formed or developed on a transfer element (e.g., a photoconductor drum) during an imaging process. A sensor measures the amount of marking agent present on the patch. The measured amount of marking agent is then compared to a known parameter to determine if the calibration patch actually contains the expected density or percentage fill of marking agent.
If the measured amount of marking agent is more or less than expected, the printing process is adjusted to provide an increase or decrease in the amount of marking agent used during the imaging process to compensate for the difference. Thus, the calibration procedure helps to maintain print quality by monitoring the amount of marking agent being used in the imaging portion of the EP printing process.
However, the calibration procedure used in conventional EP printing devices has some disadvantages. One disadvantage is that the current calibration procedure is premised on the assumption that all the marking agent developed on a transfer element (e.g., a photoconductor drum) during an imaging process actually transfers to the print medium during a transfer process. In the described calibration procedure, the density of the calibration patch is measured when the patch is on the transfer element. The patch does not transfer to a print medium, and there is no determination made as to the amount of marking agent that ultimately transfers to the print medium. Thus, the calibration procedure only measures the density or amount of marking agent that is developed on the transfer element. It does not measure the amount of marking agent that actually ends up on the print medium.
The calibration procedure is therefore inaccurate to the extent that the transfer process is imperfect. That is, although the calibration procedure accounts for anomalies up through the imaging process by comparing actual and expected marking agent densities at the transfer element, it does not account for anomalies that may exist in the image transfer process. Current calibration procedures provide no accounting of how much marking agent actually ends up on a print medium. Thus, the overall goal of maintaining print quality may be frustrated by an imprecise image transfer process despite the presence of a properly functioning calibration procedure.
Other disadvantages with current calibration procedures relate to the limited information they provide. For example, the calibration patch is a one-time use item. Once the patch is developed to and measured on the transfer element, the marking agent making up the patch is scraped off the transfer element into a waste hopper by a cleaning blade. In addition to not providing any information about how much marking agent actually transfers to a print medium, current calibration procedures do not provide any information regarding how much marking agent ends up in the waste hopper as waste.
Accordingly, the need exists for a way to calibrate an EP printing process that accounts for the amount of marking agent that actually reaches a print medium and that provides additional beneficial information about the process not currently provided by conventional calibration procedures.
A system and methods gather calibration information both before and after implementing various printing functions in an electrophotographic (EP) printing process. The printing functions are applied to a calibration patch developed on a transfer element within an EP printing device.
In one embodiment, a calibration patch is formed on an intermediate transfer element and measured to determine the density or percentage fill of the marking agent (e.g., dry toner) that makes up the patch. The calibration patch is then transferred to a print medium, and the area of the transfer element on which the patch was formed is measured again. A transferred amount of marking agent is then calculated based on the amounts of marking agent measured both before and after the transfer step.
In another embodiment, after the area of the transfer element on which the patch was formed is measured for the second time, the area is scraped with a cleaning blade to remove marking agent into a waste hopper. The area of the transfer element on which the patch was formed is then measured again. A waste amount of marking agent is then calculated based on the amounts of marking agent measured both before and after the scraping step.